...Rav Berachya said: The Jewish people, also, made an inappropriate request, and God answered them appropriately. The verse says, "Let us know, let us strive to know God; His going forth is as sure as dawn, and He will come to us like rain." God said to them: "My daughter, you ask for something [rain] which is sometimes desirable and sometimes undesirable. But I will be for you something which is always desirable." As the verse says: "I will be like dew to Israel."
[The Jewish people] made another inappropriate request. They said before him: "Master of the world, 'Place me like a seal on your heart, like a seal on your arm.' " He said to them: "My daughter, you ask for something which is sometimes seen and sometimes not seen. But I will make you into something which is always seen, as the verse says, 'Behold, I have engraved you on [my] hands.' "
I think there are two deep metaphors in this passage, well beyond the word game (building a story around minor differences between Biblical verses) which superficially looks like its basis.
About the first half of the passage:
One cannot help noting that while dew is always a good thing, unlike rain, dew is much LESS of a good thing than rain can be. Rain is the usual means of growing crops, and it is hard to impossible for crops to survive based on dew alone. I think the metaphor is that we asked for God's presence to be obvious, but God preferred that it be subtle. We wanted continous large-scale miracles through which God would provide for our material needs, like rain does. But as the Torah and Neviim Rishonim show, this method does not always produce good results. Instead, God preferred to reveal Himself to us in a manner more like dew. God is always present, but in a subtle manner, easy to miss, and not providing miracles to guarantee that our food and material needs are always met.
About the second half of the passage:
Many people, especially in recent decades, take a "buffet" style approach to religion. They are happy to perform the rituals they enjoy or find meaning in. But when it comes to something uncomfortable, or which they don't understand, they ignore the religious requirement and revert to a secular lifestyle. Their religiousness is sometimes seen, sometimes not, like a seal on one's arm. This approach is clearly enticing, and it's no wonder the Jewish people requested it. But God did not allow this. If there is to be a connection between man and God, it must be permanent. We cannot take off our kippot and become secular whenever we get the temptation to momentarily break halacha. Our religiousness must be "on God's hands", always visible, with no conditionality or opportunity for abandonment.
Rav Berachya, I just have to say, you are brilliant.